1. Field of the Invention
The invention relates to a vehicle powertrain that includes a flywheel which is connected to and disconnected from an output shaft of an engine. In particular, the invention relates to a control executed when a malfunction with respect to at least either of connection or disconnection of the flywheel occurs.
2. Description of the Related Art
In general, a flywheel is attached to a crankshaft of an engine that functions as an output shaft of the engine, in order to reduce fluctuation in rotation of the engine. If the moment of inertia of the flywheel is made larger, the fluctuation in rotation of the engine is reduced. In particular, the effect of reducing the fluctuation is significant when the engine is idling or operated at low rotational speed. On the other hand, when the vehicle is accelerated while the moment of inertia of the flywheel is large, rotational energy produced by the engine is consumed in order to accelerate rotation of the flywheel, thus deteriorating the acceleration performance of the vehicle. In addition, when the vehicle is decelerated, an engine brake does not fully work due to the rotational energy stored in the flywheel.
A flywheel whose moment of inertia can be changed has been proposed in order to reduce the fluctuation in rotation of the engine when the vehicle is traveling at low speed (the engine is operated at low rotational speed), and improve the acceleration response of the vehicle. Japanese Patent Application Publication No. 2003-074641 (No. JP-A-074641) describes a technology in which the engine is provided with a first flywheel attached to a crankshaft of the engine and a second flywheel connected to and disconnected from the first flywheel. In the technology, when the engine is idling, the second flywheel is connected to the first flywheel so as to increase the moment of inertia of the first flywheel attached to the crankshaft. Further, when the vehicle is accelerated, the second flywheel is disconnected from the first flywheel so as to reduce the moment of inertia of the first flywheel.
In the aforementioned Japanese Patent Application Publication No. 2003-074641 (JP-A-2003-074641), there is no description with respect to a control executed when a malfunction occurs, for example, when a malfunction, in which the second flywheel cannot be connected to or disconnected from the first flywheel, occurs. When such a malfunction occurs, the moment of inertia generated in the rotational system of the engine deviates from the assumed value, and therefore the desired engine performance may not be achieved.